Hub joints used for joining space frames typically include multiple assembly parts, and require significant time to assemble or disassemble using special tools. Conventional hub joints may only be assembled into a specific structure. The cost of conventional hub joints is typically high, due to components requiring machining or custom fabrication.
Space frames have increased in popularity in the last decades. This is due to better materials and computer aided design tools. Indeed, complex space frame and truss structures may be seen in many applications including amusement parks, commercial buildings, complexes, hangers, space stations, playgrounds, road signs, towers, and tents, for example.
A key component of any space frame structure is the connector or joint. The type of joint depends on the connection method (welding, bolting, etc.), the size of the joining members, and the role the space frame has in the application. Many types of joints are used for space frame structures. For example, Leung in U.S. Pat. No. 5,056,291 describes a modular system for space frame structures, in which a crystal-like hub is used to connect struts in a variety of configurations. The hub joins struts having ends equipped with C-shaped grips, which engage trunnions. The C-shaped end grips may rotate about an axis of the trunnions. A disadvantage of the Leung invention is that it requires custom manufactured components and special tooling. The Leung invention is also limited in the number of struts that may be attached to the hub. Furthermore, although the end grips snap into place, they are not locked and, hence, may unexpectedly be unsnapped.
Grimm in U.S. Pat. No. 4,676,043 describes a hub joint having elements arranged concentrically to one another. The Grimm invention forms a strong, complex, durable space frame structure. However, the Grimm invention requires custom manufactured components and special tooling, including multiple bolts and pins that have high non-recurring setup and manufacturing costs.
Some popular conventional joints include: (1) the MERO connector, (2) the UNISTRUT system, (3) the Space Deck system, (4) the Triodetic system, (5) the UNIBAT system, and (6) the NODUS system
The MERO connector, introduced in 1942, includes tubular members with threaded ends connected to a steel sphere node. The sphere node is drilled and tapped to accept the tubular members. The MERO connector is a popular connector due to its strength, elegance of assembly, and improvements including a cylindrical joint (type ZK), a plate-disc joint (type TK), a hollow semi-spherical joint (type NK), and a block joint (type BK).
The UNISTRUT system, introduced in 1955, includes a connector consisting of a pressed steel plate formed in a special tooling machine. The UNISTRUT system, which includes four components, is self aligning and self-leveling.
The Space Deck system was introduced in the United Kingdom during the 1960s as an industrialized space frame system which, when assembled at the site, produces a double-layer square-on-offset square configuration. The basic unit is an inverted square based pyramid consisting of an angle top tray and four diagonal or bracing members. Connection requires bolting top layer members and interconnecting them using tie bars. A turnbuckle is used to adjust the center camber of the structure.
A Canadian firm of F. Fentiman developed the Triodetic system, which is a popular hub joint system. This system uses an extruded aluminum hub for inserting members of any cross-section, after a deforming process to shape the ends of the members. This hub joint system effectively substitutes for welding, bolting or riveting.
S. du Chateau introduced the UNIBAT system in France in 1977. Its modular pyramidal skeletal units are bolted at their corners to adjacent units with bolts. A lower layer is formed by tubular members, which are flattened and joined by only one vertical bolt. The UNIBAT system may be used for double-layered or multi-layered structures.
The Tubes Division of the British Steel Corporation introduced the NODUS system in 1972. The joint of the NODUS system consists of two casings, with chord and fork connectors used as diagonals. The casings are held together by a center bolt. Although the NODUS system has been used in the construction of horizontal double-layer grids, it may be adapted to vertical, inclined or multi-layer grids. This system has been used throughout the world.
Common to all of the above mentioned hub joints are multiple components requiring custom manufacturing, complex assembly, and/or specialized tools. Hence, the cost of manufacturing, assembling, reconfiguring, and disassembling the aforementioned systems is high, when used in large or complex structures. Furthermore, they may only be used in specific structures for which they were originally intended. Joints and members cannot be removed after a structure is partially or fully assembled.
As will be explained, the present invention provides a simple, low cost, lightweight, strong, and durable hub joint for rapidly assembling, reconfiguring, or disassembling a frame structure. The present invention joins and secures tubular members at a vertex or a node using a low cost hub joint that requires minimal manufacturing costs with common off the shelf materials and components.
As will be explained, the present invention includes a hub joint that may be easily scaled using any size and number of tubular members, and may be used in any type of space frame structure including geodesic domes, trusses, slabs, 4-sided pyramids, 5-sided pyramids, and circular structures.